1. Field of the Invention
The present invention concerns a compressor installation with at least one water-injected volumetric compressor element, provided with a suction line and a compressed air line, driving means for this compressor element, a water cycle in which the compressor element is erected, containing a water separator erected in the compressed air line and a return line for the separated water extending between the bottom side of said water separator and the inner space of the compressor element, and a water supply device for supplying water to the water cycle containing a water supply line with a controllable valve therein and a reverse osmosis filter, a device for measuring the amount of water in said water cycle and a device for measuring the conductivity of the water in this water cycle.
2. Discussion of the Related Art
With such compressor installations, water is injected on the compressing parts of the compressor element, to cool these parts as well as to lubricate them, and to fill the gaps between the mutual compressing parts as well as the gaps between the compressing parts and the housing of the compressor element.
Each compressor element can, depending on the temperature and the humidity of the sucked-in air, consume water or produce water, which is why a water supply device is provided with which, if necessary, water is supplied to the water cycle, usually via the inlet line of the compressor element.
The supplied water must be pure, and the mineral content must be sufficiently low in order to avoid deposits on seals, valves and the like. However, the mineral content should not be too low either, since the water can become corrosive then, for example as carbonic acid from the air can no longer be absorbed in the water and will be present in the water as free carbonic acid, as a result of which the pH will drop.
The corrosive character of the water can be determined on the basis of its conductivity. In order not to be corrosive, the conductivity of the water should be between 10 and 20 xcexcS/cm at 25xc2x0 C.
Distilled water is expensive. That is why the supplied water is usually treated on site, i.e. it is demineralized in a demineralization device.
A compressor installation with such a demineralization device is described in WO-A-99/02863.
This compressor installation has a single demineralization device which can be a reverse osmosis filter as well as an ion exchanger.
The demineralization device is connected to the rest of the compressor installation via lines with valves, in such a manner that the same device can be placed in the water supply line as well as in a by-pass bridging the water cycle.
The quality of the incoming water has little influence on the life of a reverse osmosis filter, but it does influence its yield. When the quality is bad, the output of the useful permeate will drop, and the output of the concentrate, which is to be removed, will rise.
A reverse osmosis filter is not particularly fit to reduce the conductivity of the water in the water cycle. A major part of the water cycle has to be discharged as a concentrate and hence has to be replaced by fresh water which has not been treated yet, with a relatively high conductivity, whose conductivity has to be reduced in the reverse osmosis filter.
Replacing a reverse osmosis filter as a demineralization device by an ion exchanger is not much better.
An ion exchanger is very well fit to reduce the conductivity of the water cycle, since it is relatively low already, but its life can be strongly reduced when fresh water of bad quality, and thus with a high conductivity, has to be treated.
The invention aims a compressor installation which does not have the above-mentioned and other disadvantages.
This aim is reached according to the invention in that a by-pass is connected to the water cycle in which are erected an ion exchanger and a controllable valve, whereby the valve in the water supply line is controlled by the device for measuring the amount of water in the water cycle, and the valve in the by-pass is controlled by the device for measuring the conductivity of the water.
The compressor installation thus has a separate demineralization device for the fresh water which is supplied to the water cycle and for reducing the conductivity of the water in the water cycle, so that both demineralization devices can function optimally and have a long life.
The by-pass can bridge the compressor element and thus extend between the return line and the suction line.
The device for measuring the conductivity is preferably provided in the return line.
The water supply device can be connected to the suction line.
The device for measuring the amount of water in the water cycle can be a hypsometer provided in or on the water separator.